Bubbles belong to all of us, and SodaStream lets you carbonate your own water at home for pennies on the dollar.

There are way too many SodaStream models to choose from—you can see a comparison chart here—but the basic concept is the same: Cold, flat water goes in, fizzy water comes out. From there, you can add soda syrups or flavorings—I actually really like their Diet Coke clone—but you certainly don’t have to.

So how does the math work out? A single 14.5 oz. SodaStream CO2 canister will carbonate 60L of water for $15. 60L is equivalent to roughly 14 12-packs of Topo Chico. At around $7.50 each, that’s over $100 worth of water, meaning most SodaStream kits will pay for themselves in very short order, and that doesn’t even account for their positive environmental side effects.

Yes, there are some recurring costs. You’ll need to replace the special bottles every once in awhile, and the syrups run about $5 per bottle (though most make 9L each). You’ll also have to trade in your empty CO2 canister for a new one for $15 at Target, Bed Bath & Beyond, or a number of other stores, unless you hack it to accept non-proprietary canisters. But no matter what flavors you love or how often you use it, you always end up ahead vs. buying your fizzy drinks off the shelf.